1. Field of the Invention
The present invention is generally in the field of electrical circuits. More specifically, the invention is in the field of communications circuits.
2. Related Art
Multi-throw RF switches having multiple inputs and a shared output can be used in mobile communication devices, such as cellular handsets, to provide operation at more than one frequency. For example, a multi-throw RF switch can be used in a cellular handset operating in a system using a global system for mobile communications (GSM) communications standard to enable the cellular handset to operate either at a low band frequency of 900.0 MHz or a high band frequency of 1800.0 MHz by selectively coupling a corresponding input to the shared output. For multi-throw RF switches, such as multi-throw RF switches used in mobile communication devices using the GSM communications standard, there is a continuing need to reduce harmonics, such as third harmonics, generated by the switch and generated by power amplifiers that are coupled to the inputs of the switch.
A conventional multi-throw RF switch can include two or more switching arms, where each switching arm includes a number of field effect transistors (FETs) coupled in “series,” and where each switching arm is coupled to a separate input, which can be coupled to a power amplifier, and a shared output, which can be coupled to an antenna. To reduce harmonics generated by the power amplifier, a conventional filter, which is a discrete filtering device, can be coupled between the input of the RF switch and the power amplifier. Although the conventional filter can reduce the level of harmonics generated by the power amplifier, it (i.e. the conventional filter) may not provide a sufficient reduction in harmonics, such as third harmonics, generated by an RF switch, such as a multi-throw RF switch.